1. Field of the Invention
The present invention relates to a progressive forming method by a press machine, more particularly, to a progressive forming method capable of wasteless processing.
2. Description of the Prior Art
In progressive forming, a continuous strip material is intermittently moved and subjected successively to various types of processing, such as punching, slitting, forming, and finishing, to produce a continuous stream of products.
To increase the yield, it is necessary to decrease the amount of scrap or waste produced between adjacent products in the direction of supply of the strip material. Such "scrap-less" processing is easily attained when the product to be produced has a constant length in cross-section along the direction of supply. However, when the cross-sectional length is not constant, scrap-less processing is difficult.
That is, in the conventional technique, the desired cross-sectional profile of the product is obtained by one forming process. In such a forming process, there is little space for gripping the strip material in the direction of supply of the material. This, together with the fact the product to be produced has a varied length in the direction of supply, invariably results in slipping of the material. Since the cross-sectional length of the product varies in the direction of supply, the degree of slipping also varies in the direction of supply. The resultant product therefore ends up with uneven edges in that direction. Additional processing is necessary to remove the uneveness and give the product normal edges. This leads to the drawback of wasted material and a decreased yield.